Mitochondrial GrpE is present in a complex with hsp70 and preproteins in transit across membranes.

We characterized a 24-kDa protein associated with matrix hsp70 (mt-hsp70) of Neurospora crassa and Saccharomyces cerevisiae mitochondria. By using specific antibodies, the protein was identified as MGE, a mitochondrial homolog of the prokaryotic heat shock protein GrpE. MGE extracted from mitochondria was quantitatively bound to hsp70. It was efficiently released ...
from hsp70 by the addition of Mg-ATP but not by nonhydrolyzable ATP analogs or high salt. A mutant mt-hsp70, which was impaired in release of bound precursor proteins, released MGE in an ATP-dependent manner, indicating that precursor proteins and MGE bind to different sites of hsp70. A preprotein accumulated in transit across the mitochondrial membranes was specifically coprecipitated by either antibodies directed against MGE or antibodies directed against mt-hsp70. The preprotein accumulated at the outer membrane was not coprecipitated by either antibody preparation. After being imported into the matrix, the preprotein could be coprecipitated only by antibodies against mt-hsp70. We propose that mt-hsp70 and MGE cooperate in membrane translocation of preproteins.
Mesh Terms:
Ascomycota, Biological Transport, Cell Compartmentation, Fungal Proteins, Heat-Shock Proteins, Intracellular Membranes, Membrane Transport Proteins, Mitochondria, Mitochondrial Membrane Transport Proteins, Molecular Chaperones, Neurospora crassa, Protein Binding, Protein Precursors, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins
Mol. Cell. Biol.
Date: Oct. 01, 1994
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